JPH05230534A - Production of grain-oriented silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PURPOSE:To produce a grain-oriented silicon steel sheet excellent in magnetic properties by regulating the components of a slab as raw material, controlling the temp. between passes at cold rolling and the primary recrystallized grain size before finish annealing, respectively, and adding Sn, if necessary, to the raw material at the time of producing a silicon steel sheet. CONSTITUTION:A slab of a steel having a composition which contains, by weight, 0.025-0.075% C, 2.5-4.5% Si, 0.010-0.060% acid-soluble Al, <0.0030% Ni, S and Se by the amounts satisfying (S+0.405Se)<0.014%, and 0.05-0.8% Mn or further contains 0.01-0.15% Sn and where the relations between respective contents, represented by percentages, of acid-soluble Al and N a controller in the rauge of Al-27/14N>0.0100 is heated up to <1280 deg.C and hot-rolled into a plate. This plate is subjected, without annealing, to cold rolling at 60-70% draft, and the temp. between cold rolling passes is regulated to <=200 deg.C. Successively, the resulting cold rolled steel sheet is subjected to decarburizing annealing, and the average value of the primary recrystallized grain sizes in the course between the completion of annealing and the initiation of final finish annealing is regulated to 18-30mum and the steel sheet is subjected to nitriding treatment in the course between the hot rolling and the initiation of secondary recrystallization at the final finish annealing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, which is used as an iron core of a transformer or the like.

[0002]

2. Description of the Related Art Unidirectional electrical steel sheets are mainly used as iron core materials for transformers and other electrical equipment, and are required to have excellent magnetic characteristics such as excitation characteristics and iron loss characteristics. As a numerical value showing the excitation characteristic, the strength of a normal magnetic field is 80
A magnetic flux density B _{8 at} 0 A / m is used. In addition, as the numerical value showing the iron loss characteristic, the iron loss per kg when magnetized to 1.7 Tesla (T) at a frequency of 50 Hz is W _17/50.
Are using. The magnetic flux density is the most dominant factor of the iron loss characteristics, and generally speaking, the higher the magnetic flux density, the better the iron loss characteristics. Generally, when the magnetic flux density is increased, the secondary recrystallized grains become large, which may result in poor iron loss characteristics. On the other hand, by controlling the magnetic domains, the iron loss characteristics can be improved regardless of the grain size of the secondary recrystallized grains.

This unidirectional electrical steel sheet undergoes secondary recrystallization in the final finishing annealing step to develop a so-called Goss structure having {110} on the steel sheet surface and <001> axis in the rolling direction. Being manufactured. In order to obtain good magnetic properties, it is necessary to highly align <001>, which is the easy magnetization axis, in the rolling direction. Typical methods for producing such a high magnetic flux density unidirectional electrical steel sheet are methods described in Japanese Patent Publication No. 40-15644 by Satoru Taguchi et al. And Japanese Patent Publication No. 51-13469 by Takuichi Imanaka. . In the former, MnS and AlN are used as main inhibitors, and in the latter, MnS, MnSe, Sb, etc. are used. Therefore, in the current technology, it is essential to appropriately control the size, morphology and dispersion state of the precipitates that function as these inhibitors. Speaking of MnS, in the current process, when the slab is heated before hot rolling, MnS
A method is used in which the solid solution is once completely dissolved and then precipitated during hot rolling. A temperature of about 1400 ° C. is necessary to completely form a solid solution of the required amount of MnS for secondary recrystallization. This is more than 200 ℃ higher than the slab heating temperature of ordinary steel,
This high temperature slab heat treatment has the following disadvantages.

1) A high temperature slab heating furnace dedicated to grain-oriented electrical steel is required. 2) The energy intensity of the heating furnace is high. 3) The amount of molten scale increases, and the adverse effect on operation is large, as seen in so-called shaving. In order to avoid such problems, the slab heating temperature should be lowered to the level of ordinary steel, but this means that at the same time, the amount of MnS effective as an inhibitor is reduced or not used at all. , Inevitably brings about destabilization of secondary recrystallization. Therefore, in order to realize low temperature slab heating, it is necessary to strengthen the inhibitor in some form by a precipitate other than MnS to sufficiently suppress normal grain growth during finish annealing. As such inhibitors, sulfides, nitrides, oxides, grain boundary precipitation elements, and the like are conceivable. Known techniques include, for example, the following.

In Japanese Patent Publication No. 54-24685, As,
A method of controlling the slab heating temperature in the range of 1050 to 1350 ° C. by containing grain boundary segregation elements such as Bi, Sn, and Sb in the steel is disclosed, and in JP-A-52-24116, in addition to Al, Zr, Ti, B, Nb, Ta, V, C
It discloses a method for controlling the slab heating temperature in the range of 1100 to 1260 ° C. by containing a nitride forming element such as r or Mo. Further, in JP-A-57-158322, low-temperature slab heating is performed by lowering the Mn content and setting the Mn / S ratio to 2.5 or less, and further adding Cu to stabilize secondary recrystallization. The technology to do is disclosed. Techniques have also been disclosed in which improvements are made from the metallographic side in combination with the reinforcement of these inhibitors. That is, in JP-A-57-89433, S, Se, S in addition to Mn are added.
Elements such as b, Bi, Pb, Sn, and B are added, and the columnar crystal ratio of the slab and the secondary cold rolling reduction are combined to realize low temperature slab heating at 1100 to 1250 ° C. Further, in JP-A-59-190324, an inhibitor is composed mainly of Al and B and nitrogen in addition to S or Se, and secondary annealing is performed by performing pulse annealing at the time of primary recrystallization annealing after cold rolling. The technology to stabilize is released. Thus, in order to realize low temperature slab heating in the production of grain-oriented electrical steel sheets, great efforts have been made so far.

In JP-A-59-56522, Mn is 0.08 to 0.45% and S is 0.007%.
A technique for enabling low temperature slab heating by the following has been disclosed. By this method, the problem of defective linear secondary recrystallization of the product due to coarsening of the slab crystal grains during heating of the high temperature slab was solved.

[0007]

Although the method of low temperature slab heating is originally intended to reduce the manufacturing cost, it cannot be industrialized unless it is a technique of stably obtaining good magnetic characteristics. The present inventors have sought to omit hot-rolled sheet annealing in a method by low-temperature slab heating in order to further pursue both reduction of manufacturing cost and magnetic properties.

In the production of unidirectional electrical steel sheet, hot-rolled sheet annealing is usually performed for the purpose of making the structure non-uniform after hot rolling, precipitation treatment and the like. For example, in the production method using AlN as the main inhibitor, a method of controlling the inhibitor by performing precipitation treatment of AlN in hot-rolled sheet annealing is adopted as shown in JP-B-46-23820. Normally unidirectional electrical steel sheet is manufactured through the main processes such as casting-hot rolling-annealing-cold rolling-decarburization annealing-finishing annealing and requires a large amount of energy. Therefore, the manufacturing cost is also high.

In recent years, a review has been made on such a manufacturing process that consumes a large amount of energy, and there has been an increasing demand for simplifying the process and energy. In order to meet such a demand, in a production method using AlN as a main inhibitor, the precipitation treatment of AlN in hot-rolled sheet annealing is replaced by high-temperature winding after hot rolling (Japanese Patent Publication No. 59-45730). Was proposed. Certainly, even if the hot-rolled sheet annealing is omitted by this method, the magnetic characteristics can be secured to some extent, but in the ordinary method of winding in a coil shape of 5 to 20 tons, in the coil during the cooling process, Difference in the thermal history due to the location occurs, inevitably the deposition of AlN becomes non-uniform, and the final magnetic characteristics vary depending on the location in the coil, resulting in a decrease in yield.

Therefore, the present inventors have paid attention to the recrystallization phenomenon after the final hot rolling final pass, which has received little attention in the past, and utilize this phenomenon to perform cold rolling once under a high pressure of 80% or more. A method of omitting hot-rolled sheet annealing in the manufacturing method (JP-A-2-263923, JP-A-2-263924).
(See Japanese Patent Publication). These techniques are characterized in that the hot-rolled sheet has a fine recrystallized structure by being strongly pressed in the final 3 passes of hot-rolling for finishing and kept at high temperature after the end of hot-rolling. It became possible to achieve both slab heating at temperature and omitting hot-rolled sheet annealing.

By the way, in recent years, in place of the current high-grade non-oriented electrical steel sheet for use as an iron core material for turbine generators,
The need to use grain-oriented electrical steel sheets has increased. Regarding the above-mentioned applications, the unidirectional magnetic properties are more important than the applications of other non-oriented electrical steel sheets, so that the need for using grain-oriented electrical steel sheets has increased. On the other hand, the main process of manufacturing the grain-oriented electrical steel sheet after hot rolling is hot-rolled sheet annealing-cold rolling-decarburization annealing-finish annealing, which is the main step after hot rolling of non-oriented electrical steel sheet. It is more complicated than cold rolling-annealing. Therefore, in terms of manufacturing cost, the grain-oriented electrical steel sheet is considerably higher than the non-oriented electrical steel sheet.

Further, in a normal pickling line or a tandem cold rolling line, there is a limit to the plate thickness that can be passed, and if a cold rolled material having a large plate thickness is passed, breakage may occur.
Therefore, if a thick material having a thickness of 0.5 mm or the like is to be cold-rolled once, there is an upper limit to the plate thickness of the cold-rolled material, so that the cold-rolling rate needs to be low. Therefore, the present inventors
Technical development for obtaining good magnetic properties in the manufacturing method of unidirectional electrical steel sheet which is premised on slab heating at a temperature of less than 0 ° C, omission of hot-rolled sheet annealing, and cold rolling at a low pressure reduction rate. did it. Then, in the process of this technological development, they found a phenomenon in which magnetic fluctuations occur in the longitudinal direction of the coil.

As a result of detailed examination of the cause of this magnetic fluctuation, the present inventors have found that this phenomenon is due to the temperature difference in the slab during low temperature slab heating. As a result, they have found a method of eliminating the magnetic fluctuation due to the temperature difference. That is, the present invention adjusts the components of the slab, further controls the temperature of the steel sheet between passes during cold rolling, controls the average grain size of the primary recrystallized grains before finish annealing, and adds Sn to effect low-temperature slab heating and hot-rolled sheet annealing. It is intended to provide a method capable of producing a grain-oriented electrical steel sheet having excellent characteristics without magnetic fluctuation even in the production process which is omitted and has a low cold rolling reduction.

[0014]

The gist of the present invention is as follows. That is, (1)% by weight, C: 0.025 to 0.075%, S
i: 2.5-4.5%, acid-soluble Al: 0.010
0.060%, N: less than 0.0030%, S + 0.40
5Se: 0.014% or less, Mn: 0.05 to 0.8%
A slab containing Fe, the balance of which is Fe and unavoidable impurities, is heated at a temperature of less than 1280 ° C., hot-rolled, and then cold-rolled at a reduction rate of 60 to 79% without performing hot-rolled sheet annealing.
In the method for producing a grain-oriented electrical steel sheet by performing decarburization annealing and final finishing annealing, when the acid-soluble Al and N contents of the slab are Al (%) and N (%) in weight% units, Controlled within the range of the following formula, Al (%)-27 / 14N (%)> 0.0100 After hot rolling, the steel sheet is nitrided before the start of secondary recrystallization of final annealing. And a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties.

(2) C: 0.025 to 0.075% by weight, Si: 2.5 to 4.5
%, Acid-soluble Al: 0.010 to 0.060%, N:
Less than 0.0030%, S + 0.405Se: 0.014
% Or less, Mn: 0.05 to 0.8%, Sn: 0.01 to
A slab containing 0.15% and the balance consisting of Fe and unavoidable impurities is heated at a temperature of less than 1280 ° C., hot-rolled, and then hot-rolled sheet is annealed and a rolling reduction of 60 to 7 is performed.
In the method for producing a unidirectional electrical steel sheet by performing cold rolling of 9%, decarburization annealing, and final finishing annealing, the acid-soluble A of the slab is used.
The content of l and N is Al (%), N in weight% as a unit.
(%), It is controlled within the range of the following formula: Al (%)-27 / 14N (%)> 0.0100 After hot rolling, a steel sheet is formed before the start of secondary recrystallization of final finish annealing. A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties, characterized by performing a nitriding treatment.

(3) The temperature of the steel sheet between the cold rolling passes is set to 20.
The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to the above item 1 or 2, wherein the temperature is 0 ° C. or less.

(4) The magnetic particles according to any one of the above 1, 2 or 3, wherein the average grain size of the primary recrystallized grains after the completion of decarburization annealing is to be 18 to 30 μm until the start of final finish annealing. A method for producing a grain-oriented electrical steel sheet having excellent characteristics.

[0018]

The function of the grain-oriented electrical steel sheet of the present invention is
Molten steel obtained by the conventional steelmaking method is cast by a continuous casting method or an ingot making method, and if necessary, the slab is separated by a slab, and then hot-rolled into a hot-rolled sheet. It is manufactured by sequentially performing cold rolling with a rolling reduction of 60 to 79%, decarburization annealing, and final finishing annealing without performing the sheet annealing.

The inventors of the present invention have studied in detail the cause of variation in magnetism and its solution when a low temperature slab heating material is manufactured by a single cold rolling method without hot-rolled sheet annealing. As a result, we obtained a new finding that this phenomenon is caused by the variation in precipitation of AlN based on the temperature difference in the slab during slab heating, and the degree of magnetic fluctuation varies depending on the Al content and the N content.

As a solution to the problem, the N content is reduced and the Al content and the N content are suppressed within a predetermined range defined by the relational expression between them, and the steel sheet temperature between cold rolling passes is increased. Controlling the average grain size of the primary recrystallized grains from the completion of decarburization annealing to the start of final finish annealing,
It was found that adding Sn as needed was effective.

Hereinafter, these points will be described in detail.
The present inventors have paid attention to solid solution and precipitation of AlN during slab heating. At the temperature lower than 1280 ° C. which is the premise of the present invention, the complete solid solution of AlN in the α phase is not guaranteed within the Al, N and Si component ranges of the present invention. On the other hand, there are various slab heating methods, but after charging the slab into the furnace, the slab is moved from the outlet while moving with a pusher, or the slab is placed on the skid and the slab is moved from the inlet to the outlet. Etc. are generally performed. And the part of the slab that contacts the skid and the bottom of the furnace is
The temperature is often lower. Therefore, it was considered that the difference in the precipitation amount of AlN and the amount of solid solution N caused by the temperature difference in the slab occurred. In the process from hot rolling to decarburization annealing, most of the N dissolved during slab heating is Al.
Finely precipitates as N, the degree of which is solid solution N when heating the slab
It was considered to depend on the amount. In fact, when conducting an experiment in a factory, the average grain size of the primary recrystallized grains after decarburization annealing of the coil in which the magnetic characteristics fluctuated was measured using an optical microscope and an image analyzer. It was found that the diameter fluctuated. The degree of variation is Al,
It was different depending on the amount of N.

Therefore, the present inventors have considered reducing the varying amount of AlN. For that purpose, it is effective to reduce the amount of Al or N, but it is necessary to secure the amount of AlN as an inhibitor at the time of secondary recrystallization, and N can be introduced into the steel sheet by nitriding. , Al was considered to be difficult to introduce into the steel sheet, and it was considered to reduce the N content. Considering that reducing the amount of N at the steelmaking stage is technically limited or leads to cost increase, it is expected that there is a strong correlation with the amount of N dissolved in solid solution Al _R (%) = Al ( %) -27 / 14N (%)
[Al (%):% by weight of acid-soluble Al, N (%):% by weight of N] is defined, and the relationship between N (%), Al _R (%) and fluctuations in magnetic properties is defined as follows. It was investigated based on the experiment.

That is, by weight, C = 0.045%, S
i = 3.01%, acid-soluble Al = 0.10 to 0.05
7%, N = 0.003 to 0.0118%, S = 0.0
A slab having a thickness of 250 mm containing 07% and Mn = 0.14% and the balance Fe and unavoidable impurities was prepared.
Then, each slab was soaked at 2 levels of temperature of 1100 ° C. and 1200 ° C. for 60 minutes and then hot-rolled in 11 passes to have a thickness of 2.0 mm, water-cooled after about 2 seconds, cooled to 550 ° C., and then wound 550 The temperature of ° C was maintained for 1 hour.

About 75% of the hot-rolled sheet was rolled without annealing the hot-rolled sheet to obtain a cold-rolled sheet having a final sheet thickness of 0.50 mm. This cold-rolled sheet was kept at 830 ° C for 300 seconds, then decarburized by keeping it at 875 ° C for 20 seconds, and then kept at 750 ° C for 30 seconds during annealing.
₃ gas was introduced to make the steel sheet absorb nitrogen. The amount of N after this nitriding treatment is 0.0193 to 0.0212% by weight.
Met. An annealing separator containing MgO as a main component was applied to the steel sheet after the nitriding treatment, and final finish annealing was performed. After that, the magnetic flux density B _{8 of the} product was measured, and the difference ΔB of B ₈ between the two slab soaking conditions taken for the slab of the same composition
₈ - seeking [B ₈ in slab heating temperature _{1100 ℃ (T) B 8 (} T) at the same temperature 1200 ° C.], shown in Figure 1.

As is apparent from FIG. 1, N (%) <0.
In the range of 0030, Al _R (%)> 0.0100, the magnetic flux density difference ΔB of the product due to the slab heating temperature difference
₈ (T) is less than 0.02T. The present inventors consider the mechanism of the phenomenon shown in FIG. 1 as follows.

In this experiment, a phenomenon caused by a temperature difference in the slab in the heating furnace was simulated by changing the slab heating temperature. According to this, in the composition range of Al and N of the present invention, under the slab heating temperature condition of less than 1280 ° C., a difference occurs in the solid solution and precipitation amount of AlN between the high temperature portion and the low temperature portion of the slab. That is, a large amount of solid solution N is present in the high temperature slab during slab heating, and during subsequent hot rolling and decarburization annealing, this solid solution N is finely precipitated in the form of AlN. On the other hand, the amount of solid solution N is small in the low temperature portion of the slab during heating of the slab, and the amount of AlN finely precipitated during the subsequent hot rolling and decarburization annealing is small. Such local nonuniformity of AlN precipitation causes local nonuniformity of grain growth of primary recrystallized grains during decarburization annealing. That is, in the portion corresponding to the high temperature portion in the slab during heating of the slab, since the amount of fine AlN during decarburization annealing is large, grain growth of primary recrystallized grains is suppressed. On the other hand, in the portion corresponding to the low temperature portion in the slab during heating of the slab, since the fine AlN is small during decarburization annealing, the primary recrystallized grains are likely to grow. For this reason, when the decarburization annealing is completed, there is a spatial nonuniformity of the primary recrystallized grain size in the coil due to the temperature difference in the slab during the heating of the slab. As disclosed by the present inventors in Japanese Patent Application Laid-Open No. 2-182866, the primary recrystallized grain size at the completion of decarburization annealing has an extremely strong correlation with the magnetic flux density of the product. Therefore, the spatial nonuniformity of the primary recrystallized grain size causes the spatial nonuniformity of the magnetic flux density in the product. Therefore, if the variation in the amount of solid solution N in the slab during heating of the slab, which causes the variation in the magnetic flux density, is set within a predetermined range, it is considered that the variation in the magnetic flux density of the product is reduced.

Next, the reasons for limiting the constituent features of the present invention will be described. First, the reasons for limiting the slab components and the slab heating temperature will be described in detail. C is 0.025% by weight
If it is less than (hereinafter simply abbreviated as%), the secondary recrystallization becomes unstable, and even if secondary recrystallization is performed, B ₈ > 1.80.
Since (T) is hard to obtain, it was set to 0.025% or more. on the other hand,
If the amount of C is too large, the decarburization annealing time becomes long and it is not economical, so the content was made 0.075% or less.

If Si exceeds 4.5%, cracking during cold rolling becomes significant, so the content of Si is set to 4.5% or less. On the other hand, if it is less than 2.5%, the specific resistance of the material is too low, and the low iron loss required for the transformer core material cannot be obtained.
It is preferably 3.2% or more. In order to secure AlN or (Al, Si) N necessary for stabilizing the secondary recrystallization, Al needs to be 0.010% or more as acid-soluble Al. If the acid-soluble Al exceeds 0.060%, the AlN of the hot-rolled sheet becomes unsuitable and the secondary recrystallization becomes unstable, so the content was made 0.060% or less.

As for the N content, as shown in FIG.
It should be less than 0030%. And, this is effective in reducing the fluctuation of magnetism due to the temperature deviation during slab heating. The lower limit of the amount of N is not particularly limited, but it is industrially difficult to make N 0.0001% or less in the steelmaking stage. As shown in FIG. 1, the amounts of acid-soluble Al and N are Al _R = Al-27 / 14N> 0.
It is necessary to set it to 0100. This is also effective in reducing fluctuations in magnetism due to temperature deviation during slab heating. The upper limit of Al _R = Al-27 / 14N is determined from the regulation of the amount of acid-soluble Al and N, but is 0.06.
Permissible up to 0%.

Even if MnS and MnSe are present in the steel, it is possible to improve the magnetic properties by properly selecting the conditions of the manufacturing process. However, if S and Se are high, secondary recrystallization defects called linear fine grains tend to occur. S equivalent = S + 32 / 79Se = S + 0.405
Se was defined and the relationship between this and the secondary recrystallization defect rate was investigated. In order to prevent the occurrence of this secondary recrystallization defect portion, (S + 0.405Se) ≦ 0.014% should be satisfied. If S or Se exceeds the above value, the probability of occurrence of secondary recrystallization defects will be high no matter how the manufacturing conditions are changed, and the time required for purification by final annealing will be too long, which is preferable. Not from this perspective, S
Alternatively, there is no point in unnecessarily increasing Se.

The lower limit of Mn is 0.05%. 0.0
If it is less than 5%, problems such as a defective shape (flatness) of the hot-rolled sheet obtained by hot rolling and a corrugated side edge portion of the strip and a reduction in product yield occur. On the other hand, Mn
If the amount exceeds 0.8%, the magnetic flux density of the product decreases, which is not preferable, so the upper limit of the Mn amount was made 0.8%. Sn
Is known as a grain boundary segregation element and is an element that suppresses grain growth. On the other hand, Sn is completely dissolved during heating of the slab, and it is considered that Sn is evenly dissolved within the slab during heating having a temperature difference of several tens of degrees Celsius which is usually considered. Therefore, it is considered that Sn, which is uniformly distributed in the slab during heating despite the temperature difference, also acts locally in terms of the grain growth suppressing effect during decarburization annealing. Therefore, it is considered that Sn has the effect of diluting the nonuniformity of grain growth during decarburization annealing due to the nonuniformity of precipitation of AlN. Therefore, in addition to the technique of the present invention for limiting the amount of N and the amount of Al _R , the temperature control of the steel sheet between the cold rolling passes described below, and the control of the primary recrystallized grain size, the addition of Sn is more effective for the product. This is effective in reducing the spatial variation in magnetic characteristics. The proper range of this Sn is 0.01
˜0.15%. Below this lower limit, the grain growth suppressing effect is too small, which is not preferable. On the other hand, if the upper limit is exceeded, nitriding of the steel sheet becomes difficult, which causes secondary recrystallization failure, which is not preferable.

In addition to these, a small amount of Sb, Cu, Cr, Ni, B, Ti, Nb, etc., which are known as inhibitor constituent elements, may be contained. Especially B, Ti, N
The nitride constituent elements such as b are caused by the temperature difference in the slab.
It may be positively added in order to reduce the spatial nonuniformity of 1N precipitation. The slab heating temperature was limited to less than 1280 ° C. for the purpose of cost reduction in the same manner as ordinary steel. It is preferably 1200 ° C or lower.

The heated slab is subsequently hot rolled to form a hot rolled plate. The hot rolling method is not particularly limited, but the hot rolling end temperature is set to 850 to 1050.
It is more preferable that the temperature is set to 0 ° C. and the cumulative rolling reduction in the final pass of hot rolling is set to 40% or more in order to reduce the local variation in the magnetism of the product and improve the magnetism. After the final pass of hot rolling, it is usually air-cooled for about 0.1 to 100 seconds, water-cooled, wound at a temperature of 300 to 700 ° C., and gradually cooled.
The cooling process is not particularly limited, but air cooling for 1 second or more after hot rolling is preferable for promoting recrystallization and stabilizing magnetism at a high level. This hot-rolled sheet was continuously subjected to a rolling reduction of 60 without annealing the hot-rolled sheet.
Cold rolling of ~ 79% is performed to obtain the final cold rolled sheet.

The reduction ratio is defined as 60 to 79% because, when the cold-rolled sheet has a large thickness such as 0.5 mm, when the reduction ratio is 80% or more, the cold-rolled material (hot-rolled sheet) is naturally used. Is too thick, and it is not preferable because it easily breaks when passing through the pickling line or the cold rolling line. On the other hand, the lower limit value is defined because it is necessary to keep the magnetic flux density at a high level. It is preferable to keep the temperature of the steel sheet between the cold rolling passes at 200 ° C. or lower in order to maintain the magnetic flux density at a high level in the case of the low cold rolling rate as in the present invention. The present inventors presume about this mechanism as follows. Conventionally, the cold rolling rate is known as a controlling factor of the cold rolling recrystallization texture, and in particular, {110} <001> as a controlling factor for the secondary recrystallization orientation,
The abundance of {111} <112> oriented grains is important. The {110} <001> oriented grains in the recrystallized texture are
It becomes maximum at a reduction rate of 60 to 70%, and decreases in the reduction rate range of more than 70% as the reduction rate increases. On the other hand, the {111} <112> oriented grains in the recrystallized texture tend to increase in the rolling reduction range up to about 90% as the rolling reduction increases. On the other hand, interpass aging in cold rolling tends to promote the formation of deformation zones during cold rolling and increase the {110} <001> oriented grains nucleating from the deformation zones in the recrystallization texture. On the other hand, this interpass aging tends to reduce the amount of {111} <112> oriented grains present in the recrystallized texture. Therefore, {110} <001>
From the viewpoint of the abundance of the oriented grains and the {111} <112> oriented grains in the recrystallized texture, the inter-pass aging has the same effect as the reduction of the cold rolling reduction.
Therefore, in order to bring a recrystallized texture that is usually obtained at a high cold rolling rate of 80% or more to a cold rolling rate of less than 80% as close as possible, the effect of interpass aging as in the present invention is minimized. Elimination is considered effective.

The cold rolling method is not particularly limited. Either the tandem method or the reverse method may be used. It is sufficient to keep the temperature between passes at 200 ° C or lower. Although the number of passes is not particularly limited,
It makes no sense to take more than 100 passes unnecessarily. The steel sheet after such cold rolling is subjected to decarburization annealing, annealing separation agent coating, and final finishing annealing by a usual method to obtain a final product. Here, it is more preferable to control the average particle size of the primary recrystallized grains to 18 to 30 μm after the completion of decarburization annealing and before the start of final finish annealing, in addition to controlling the amounts of N and Al _R.
The reason is that it is easy to obtain a good magnetic flux density in this range of the average particle size, and the change of the magnetic flux density due to the particle size variation is small.

It is defined that the steel sheet is subjected to the nitriding treatment before the secondary recrystallization of the final finish annealing after the hot rolling.
This is because the inhibitor strength required for secondary recrystallization tends to be insufficient in the process that is premised on low temperature slab heating as in the present invention. The method of nitriding is not particularly limited, and it is a method of mixing NH ₃ gas into the annealing atmosphere after decarburization annealing to perform nitriding, a method of using plasma, a nitride is added to an annealing separating agent, and a final finishing annealing is performed. Any method may be used, such as a method of absorbing nitrogen generated by decomposition of nitrides in the temperature into the steel sheet, or a method of nitriding the steel sheet by increasing the N ₂ partial pressure in the atmosphere of final annealing. The nitriding amount is not particularly limited, but 1 ppm or more is necessary.

[0037]

EXAMPLES Examples will be described below. Example 1 C: 0.051 wt%, Si: 3.10 wt%, Mn:
0.14% by weight, S: 0.006% by weight, acid-soluble A
1: 0.034% by weight as a basic component and N content of 0.0
081% by weight, 0.0062% by weight, 0.0025
%, 0.0013% by weight added at 4 levels, the balance being Fe and unavoidable impurities of 4 types of 250 mm
Created a thick slab. In this case, Al _R (%) is 0.
0184% by weight, 0.0220% by weight, 0.029
It was 2% by weight and 0.0315% by weight.

Such a slab was a: 1180 ° C., b: 11
After soaking for 60 minutes at two levels of temperature of 10 ° C., hot rolling was immediately started, and 40 mm thickness was obtained by 5 passes and then 2.
A hot rolled plate having a thickness of 3 mm was used. Then, after the hot rolling was finished, a coiling simulation was performed in which the material was air-cooled for 1 second, water-cooled to 550 ° C., held at 550 ° C. for 1 hour, and then furnace-cooled.

The hot-rolled sheet was pickled to form a cold-rolled sheet having a rolling reduction of about 78% and a length of 0.50 mm, and subjected to decarburization annealing at 820 ° C. for 300 seconds. After that, annealing was carried out at 750 ° C. for 30 seconds, NH ₃ gas was mixed in the annealing atmosphere, and the steel sheet was made to absorb nitrogen. N of this steel sheet after nitriding
The amount was 0.0198-0.0214% by weight. Then, an annealing separator containing MgO as a main component was applied to this steel sheet, and the temperature was kept at 15 ° C. in an atmosphere gas of N ₂ 25% and H ₂ 75%.
The temperature was raised to 1200 ° C at the same time, and then H ₂ 100 was added.
% Final atmosphere annealing was carried out at 1200 ° C. for 20 hours in an atmosphere gas.

The experimental conditions and the results of the magnetic properties are shown in Table 1.
The comparative examples (No. 1 to 4) have a large difference in magnetic characteristics (B ₈ ) depending on the slab heating conditions, but the present invention (No. 5 to 8)
In the case of, the difference is small.

[0041]

[Table 1]

Example 2 C: 0.041% by weight, Si: 3.25% by weight, Mn:
0.15% by weight, S: 0.007% by weight, N: 0.00
22% by weight as a basic component, acid-soluble Al is 0.0
13 levels, 0.019% by weight, 0.025% by weight, 0.037% by weight, added at 4 levels,
4 types of 250m consisting of balance Fe and unavoidable impurities
An m-thick slab was created. In this case Al _R (%) is
0.0088% by weight, 0.0148% by weight, 0.0
It was 208% by weight and 0.0328% by weight.

The slab is a: 1170 ° C., b: 11
After soaking at two levels of temperature of 00 ° C. for 60 minutes, hot rolling was immediately started, and 40 mm thickness was obtained by 5 passes and then 2.
A hot rolled sheet having a thickness of 0 mm was used. Next, this hot rolled sheet was treated under the conditions of Example 1 until the final finish annealing. In this case, the cold rolling reduction is 75%, and the N amount after nitriding is 0.0195 to
It was 0.0212% by weight.

Table 2 shows the experimental conditions and the magnetic properties of the products.
The comparative examples (Nos. 1 and 2) have a large difference in magnetic characteristics (B ₈ ) depending on the slab heating conditions, but the present invention (Nos. 3 to N).
o. In the case of 8), the difference is small.

[0045]

[Table 2]

Example 3 C: 0.044% by weight, Si: 3.28% by weight, Mn:
0.14% by weight, S: 0.007% by weight, acid-soluble A
1: 0.028 wt%, N: 0.0025 wt% (Al _R : 0.0232 wt%), a 40 mm thick slab consisting of the balance Fe and unavoidable impurities, a: 115
After heating at a temperature of 0 ° C. and b: 1100 ° C., hot rolling was performed in 6 passes to obtain a hot rolled plate of 2.3 mm. At this time, the reduction distribution is 4
0 → 24 → 16 → 11 → 6.6 → 3.9 → 2.3 (m
m).

Thereafter, the hot rolled sheet was pickled, and then cold rolled in the same direction at a rolling reduction of 78% to obtain a cold rolled sheet having a thickness of 0.50 mm. At this time, when the thickness is 1.5 mm and 1.0 mm,
Two types of cold-rolled sheets were prepared, one without aging treatment and the other with aging treatment of 250 ° C. × 5 minutes (soaking). Then 820
Decarburization annealing was performed at 300 ° C. for 300 seconds and 870 ° C. for 20 seconds. Then, during the heat treatment of holding at 750 ° C. for 30 seconds, NH ₃ gas was mixed into the atmosphere gas to cause the steel sheet to absorb nitrogen. At this time, the N content of the steel plate is 0.0208
Was 0.0221% by weight.

Next, an annealing separator containing MgO as a main component was applied to the steel sheet after the nitriding treatment, and final finish annealing was performed by a known method. Table 3 shows the experimental conditions and the magnetic properties of the products. When the aging treatment is performed (Nos. 3 to 4), the difference in the magnetic characteristics (B ₈ ) depending on the slab heating conditions is larger than when the aging treatment is not performed (Nos. 1 to 2).

[0049]

[Table 3]

Example 4 C: 0.041% by weight, Si: 3.15% by weight, Mn:
0.14% by weight, S: 0.006% by weight, acid-soluble A
l: 0.036 wt% and N: 0.0020 wt% were added to prepare a slab consisting of the balance Fe and inevitable impurities. In this case, Al _R (%) was 0.0321% by weight.

Such a slab was subjected to a: 1150 ° C., b: 10
After soaking at two levels of temperature of 90 ° C. for 60 minutes, hot rolling was started immediately, the thickness was 40 mm in 5 passes, and 1.
It was a hot rolled plate having a thickness of 8 mm. Then, the hot-rolled sheet is pickled to make a cold-rolled sheet of 0.40 mm with a reduction rate of about 78%,
Decarburization annealing was performed by holding each temperature of 00 ° C, 820 ° C, 840 ° C, and 850 ° C for 250 seconds. After that, 75
Annealing is carried out by holding at 0 ° C for 30 seconds.
₃ gases were mixed in to cause the steel sheet to absorb nitrogen. The N content of this steel sheet after nitriding was 0.0198 to 0.0211% by weight. Then, the average crystal grain size of this steel sheet was measured using an optical microscope and an image analyzer.

Then, an annealing separator containing MgO as a main component was applied to this steel sheet, and the temperature was raised to 1200 ° C. at a rate of 10 ° C./hour in an atmosphere gas of N ₂ 50% and H ₂ 50%, and then continued. The final finish annealing was carried out by holding at 1200 ° C. for 20 hours in a H ₂ 100% atmosphere gas. Table 4 shows the experimental conditions and the magnetic properties of the products.

The primary recrystallized grain size falls within a predetermined range (18 to 30).
.mu.m) (No. 3 to 6), the magnetic characteristics (B.sub.8) due to the slab heating conditions are different from those in the case of not controlling (No. 1 to 2, No. 7 to ₈ ). It can be made even smaller.

[0054]

[Table 4]

Example 5 C: 0.054% by weight, Si: 3.23% by weight, Mn:
0.15% by weight, S: 0.007% by weight, acid-soluble A
1: 0.038% by weight, N: 0.0021% by weight as a basic component, and no Sn amount added (<0.01% by weight),
It is added at three levels of 0.05% by weight and 0.14% by weight.
A 0 mm thick slab was created. In this case Al _R (%)
Was 0.0340% by weight.

Such a slab was subjected to a: 1160 ° C., b: 10
After soaking at 2 levels of temperature of 80 ° C. for 60 minutes, hot rolling was immediately started, and after 5 passes to 40 mm thickness, 2.
A hot rolled plate having a thickness of 3 mm was used. Then, this hot-rolled sheet was treated under the conditions of Example 1 until the final finish annealing. However, the decarburization annealing conditions are 800 ° C. × 250 seconds (soaking), 8
It was carried out at 20 ° C. for 250 seconds (soaking). The amount of N after nitriding is
It was 0.0184 to 0.0201% by weight.

Table 5 shows the experimental conditions and the magnetic properties of the products.
Compared with the case where Sn is not added (Nos. 1 to 4), the case where Sn is added (Nos. 5 to 12) can make the difference in magnetic characteristics (B ₈ ) depending on the slab heating conditions smaller. I can.

[0058]

[Table 5]

[Example 6] C: 0.038% by weight, S
i: 3.00% by weight, Mn: 0.16% by weight, S: 0.
007% by weight, acid-soluble Al: 0.029% by weight, N:
40 mm containing 0.0020 wt% (Al _R : 0.0251 wt%), balance Fe and unavoidable impurities
After heating the thick slab at a temperature of a: 1150 ° C and b: 1100 ° C, hot rolling is started at 1050 ° C, and 40 → 23.
→ 14 → 9 → 6 → 3.5 → 2.0 (mm) hot rolling was performed to obtain a hot rolled sheet.

Thereafter, the hot rolled sheet was pickled and then cold rolled at a rolling reduction of 75% to obtain a cold rolled sheet having a thickness of 0.50 mm.
At this time, when the thickness is 1.2 mm, no aging treatment, 110
Three types of cold-rolled sheets that had been subjected to three types of aging treatments of ℃ × 2 minutes (soaking) and 300 ℃ × 2 minutes (soaking) were prepared. Then, decarburization annealing was carried out at 820 ° C. for 300 seconds and at 860 ° C. for 20 seconds. Then, during the heat treatment of holding at 770 ° C. for 30 seconds, NH ₃ gas was mixed into the atmosphere gas to cause the steel sheet to absorb nitrogen. At this time, the N content of the steel sheet was 0.
It was 0194 to 0.0221% by weight. The average grain size of the primary recrystallized grains of this steel sheet was 23 to 25 μm when measured using an optical microscope and an image analyzer.

Then, an annealing separator containing MgO as a main component was applied to the steel sheet after the nitriding treatment, and final finish annealing was performed by a known method. Table 6 shows the experimental conditions and the magnetic properties of the products. When the aging temperature of the cold-rolled sheet is controlled within the specified range (N
o. 3-4) or without aging treatment (No. 1-2)
In comparison with the case where the aging temperature is out of the predetermined range (Nos. 5 to ₆ ), the difference in the magnetic characteristics (B ₈ ) depending on the slab heating conditions can be reduced.

[0062]

[Table 6]

[0063]

As described above, in the present invention, the amount of N, the amount of Al _R , (Al _R = Al-27 / 14N)
To control the temperature of the steel sheet between cold rolling passes,
Furthermore, by controlling the average grain size of the primary recrystallized grains after the completion of decarburization annealing and before the start of final finishing annealing, and further by adding Sn, hot-rolled sheet annealing can be omitted and good magnetic properties can be obtained. Can be stably obtained without spatial variation due to temperature deviation of the slab during slab heating, and therefore its industrial effect is extremely large.

[Brief description of drawings]

FIG. 1 Amount of N and Al _R (Al _R = Al-27 / 14
It is a graph showing the relationship between N) and the magnetic property difference resulting from the slab heating temperature difference.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] February 4, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

That is, by weight, C = 0.045%, S
i = 3.01%, acid-soluble Al = 0.10 to 0.05
7%, N = 0.003 to 0.0118%, S = 0.0
A slab having a thickness of 250 mm containing 07% and Mn = 0.14% and the balance Fe and unavoidable impurities was prepared.
Then, each slab was soaked for 60 minutes at two levels of temperature of 1100 ° C. and 1200 ° C., hot rolled in 11 passes to a thickness of 2.0 mm, water-cooled after about 2 seconds, cooled to 550 ° C. , and then 55
The temperature of 0 ° C was maintained for 1 hour.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0053

[Correction method] Change

[Correction content]

The average grain size of the primary recrystallized grains is within a predetermined range (1
8 to 30 μm) (No. 3 to 6),
It is possible to further reduce the difference in magnetic characteristics (B ₈ ) depending on the slab heating conditions, as compared with the case where no control is performed (No. 1 to 2, No. 7 to ₈ ).

Claims (4)

[Claims] 1. By weight%, C: 0.025 to 0.075%, Si: 2.5 to 4.5%, acid soluble Al: 0.010 to 0.060%, N: 0.0030% Less than S + 0.405Se: 0.014% or less, Mn: 0.05 to 0.8%, and the remaining part is a slab consisting of Fe and inevitable impurities, heated at a temperature of less than 1280 ° C., and hot rolled, Then, cold rolling with a rolling reduction of 60 to 79% without annealing the hot rolled sheet,
In the method for producing a grain-oriented electrical steel sheet by performing decarburization annealing and final finishing annealing, when the acid-soluble Al and N contents of the slab are Al (%) and N (%) in weight% units, Controlled within the range of the following formula, Al (%)-27 / 14N (%)> 0.0100 After hot rolling, the steel sheet is nitrided before the start of secondary recrystallization of final annealing. And a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties. 2. By weight%, C: 0.025 to 0.075%, Si: 2.5 to 4.5%, acid soluble Al: 0.010 to 0.060%, N: less than 0.0030%. S + 0.405Se: 0.014% or less, Mn: 0.05 to 0.8%, Sn: 0.01 to 0.15%, and a balance of Fe and unavoidable impurities in the balance is less than 1280 ° C. At the temperature of 60% to 79% without hot-rolled sheet annealing.
In the method for producing a grain-oriented electrical steel sheet by performing decarburization annealing and final finishing annealing, when the acid-soluble Al and N contents of the slab are Al (%) and N (%) in weight% units, Controlled within the range of the following formula, Al (%)-27 / 14N (%)> 0.0100 After hot rolling, the steel sheet is nitrided before the start of secondary recrystallization of final annealing. And a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties. 3. The method for producing a grain-oriented electrical steel sheet having excellent magnetic properties according to claim 1, wherein the temperature of the steel sheet between cold rolling passes is set to 200 ° C. or lower. 4. The magnetic material according to claim 1, wherein the average grain size of the primary recrystallized grains after the completion of decarburization annealing and before the start of final finishing annealing is 18 to 30 μm. A method for producing a grain-oriented electrical steel sheet having excellent characteristics.